Steering Clutch Assist Torque Control for Vibration Suppression
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Solution Overview
Problem
During autonomous driving, when a steer-by-wire system is assessed to be abnormal and transitions to assisted-control mode, the engagement of the clutch can cause a difference in angular velocity between the steering wheel and turnable wheels, leading to torsion in the torque sensor and vibrations in the steering wheel, resulting in discomfort for the driver.
Innovation Solution
A method and device that limit the assist torque to a value corresponding to the detected torque from the torque sensor until a prescribed fade-in period has passed, which corresponds to the difference in angular velocity between the steering wheel and turnable wheels, when transitioning from steer-by-wire mode under autonomous driving to assisted-control mode under manual driving.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the clutch is engaged during autonomous driving control when a difference in angular velocity has arisen between the steering wheel and turnable wheels, then the steering system transitions to assisted-control mode, but torsion is produced in the torque sensor and vibrations occur in the steering wheel
Solution Approach 1:
The control device limits assist torque before the fade-in period ends, preventing vibration from occurring in the first place. By proactively controlling the assist torque output during the fade-in period, the system avoids the torsion and vibration that would otherwise occur when the clutch is engaged with angular velocity difference.
Solution Approach 2:
The assist torque acts as an intermediary element between the clutch engagement and the steering wheel. By controlling and limiting this intermediate force during the fade-in period, the system prevents the direct transmission of torsion and vibration to the steering wheel, thereby reducing driver discomfort.
2Ease of operation
If the assist torque is immediately applied after clutch engagement, then steering assistance is provided promptly, but the vibration is amplified and driver discomfort increases
Solution Approach 1:
The assist torque is applied periodically through the fade-in period rather than immediately and continuously. The control device sets a predetermined fade-in period after clutch engagement and limits assist torque during this period, creating a time-based periodic control pattern that allows vibration to subside before full assist torque is applied.
Solution Approach 2:
The control device provides cushioning by limiting assist torque during the fade-in period before full steering assistance is restored. This beforehand cushioning prevents the harsh transmission of vibration and torsion to the driver, creating a smoother transition into full assisted-control mode.
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
Provided is a vehicle steering control method with which vibration of the steering wheel is suppressed when a clutch is engaged while turning and with which it is possible to suppress a sense of discomfort imparted to the driver. In this vehicle steering control method, when transitioning from a steer-by-wire mode under an autonomous driving mode in which a steering clutch (3), through which a steering wheel (1) and left and right front wheels (5, 6) are mechanically disconnected and connected, is disengaged, to an EPS control mode under a manual driving mode in which the steering clutch (3) is engaged and an assist torque that corresponds to a detected torque from a torque sensor (20) is imparted to the left and right front wheels (5, 6), the steering clutch (3) is engaged, and the assist torque is limited to a value that corresponds to the detected torque from the torque sensor (20) from when the steering clutch (3) is engaged until a prescribed limitation period has passed.